This is a note to let you know that I've just added the patch titled
ARM: 7653/2: do not scale loops_per_jiffy when using a constant delay clock
to the 3.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
arm-7653-2-do-not-scale-loops_per_jiffy-when-using-a-constant-delay-clock.patch
and it can be found in the queue-3.8 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From 70264367a243a68b1d5636ffb570183449803cbe Mon Sep 17 00:00:00 2001
From: Nicolas Pitre <[email protected]>
Date: Mon, 18 Feb 2013 16:36:13 +0100
Subject: ARM: 7653/2: do not scale loops_per_jiffy when using a constant delay
clock
From: Nicolas Pitre <[email protected]>
commit 70264367a243a68b1d5636ffb570183449803cbe upstream.
When udelay() is implemented using an architected timer, it is wrong
to scale loops_per_jiffy when changing the CPU clock frequency since
the timer clock remains constant.
The lpj should probably become an implementation detail relevant to
the CPU loop based delay routine only and more confined to it. In the
mean time this is the minimal fix needed to have expected delays with
the timer based implementation when cpufreq is also in use.
Reported-by: Viresh Kumar <[email protected]>
Signed-off-by: Nicolas Pitre <[email protected]>
Tested-by: Viresh Kumar <[email protected]>
Acked-by: Liviu Dudau <[email protected]>
Signed-off-by: Russell King <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
arch/arm/include/asm/delay.h | 1 +
arch/arm/kernel/smp.c | 3 +++
arch/arm/lib/delay.c | 1 +
3 files changed, 5 insertions(+)
--- a/arch/arm/include/asm/delay.h
+++ b/arch/arm/include/asm/delay.h
@@ -24,6 +24,7 @@ extern struct arm_delay_ops {
void (*delay)(unsigned long);
void (*const_udelay)(unsigned long);
void (*udelay)(unsigned long);
+ bool const_clock;
} arm_delay_ops;
#define __delay(n) arm_delay_ops.delay(n)
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -693,6 +693,9 @@ static int cpufreq_callback(struct notif
if (freq->flags & CPUFREQ_CONST_LOOPS)
return NOTIFY_OK;
+ if (arm_delay_ops.const_clock)
+ return NOTIFY_OK;
+
if (!per_cpu(l_p_j_ref, cpu)) {
per_cpu(l_p_j_ref, cpu) =
per_cpu(cpu_data, cpu).loops_per_jiffy;
--- a/arch/arm/lib/delay.c
+++ b/arch/arm/lib/delay.c
@@ -77,6 +77,7 @@ void __init register_current_timer_delay
arm_delay_ops.delay = __timer_delay;
arm_delay_ops.const_udelay = __timer_const_udelay;
arm_delay_ops.udelay = __timer_udelay;
+ arm_delay_ops.const_clock = true;
delay_calibrated = true;
} else {
pr_info("Ignoring duplicate/late registration of
read_current_timer delay\n");
Patches currently in stable-queue which might be from [email protected]
are
queue-3.8/arm-7653-2-do-not-scale-loops_per_jiffy-when-using-a-constant-delay-clock.patch
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